1. Field of the Invention
This invention relates to a terminal within an ignition circuit of an internal combustion engine and, more specifically, to such a connector in the form of an extender or an end of an ignition cable having a temperature-resistant insulating housing.
2. Summary of the Background Information
A reciprocating internal combustion engine that is not a Diesel engine includes an ignition system providing electrical current at a very high voltage to a number of spark plugs in order to ignite a mixture of fuel and air within a number of cylinders, with the electrical current being generated within a coil and delivered to the spark plugs as pulses synchronized with the rotation of a crankshaft within the engine. An internal combustion turbine engine typically includes an ignition system providing a high-voltage electrical current to one or more igniter plugs, with the electrical power being applied only to start the engine, and later, if necessary, to restart the engine in the event of a flame-out. In either case, electrical current is supplied to each spark plug or to each igniter through an ignition cable extending from a power source. Because of voltages present within the ignition cable, conductive structures within the cable, including both a wire portion and connection hardware, must be insulated to prevent arcing or leakage currents to various adjacent conductive surfaces. Because of the location of the cable adjacent to the engine, materials used for insulation must withstand high temperatures and chemicals resulting from the combustion of fuel as well as high voltages.
Ignition cables include conductive connection structures that are required to make electrical and mechanical connections at each end. Conventionally, these structures are covered with insulating housings composed of PTFE (polytetrafluoroethylene), ceramic material, silicone rubber, and PPA (polyphthalamide). These conventional materials all have disadvantages. For example, PTFE is expensive due to the cost of the material and due to the machining operations that may be required to form suitable insulating housings, while at temperatures above 450 deg F. PTFE is known to become gelatinous, causing insulating housings to deform, leading to mechanical and dielectric failures. Insulating housings composed of PPA, which has a maximum service temperature of only 329 deg F., used with engines burning natural gas have been known to fail due to the effects of high operating temperatures. Silicone rubber is not compatible with steam or petroleum based materials and is susceptible to heat embrittlement.
FIG. 1 is a longitudinal cross-sectional view of a conventional extender 10, which is provided to bring the electrical connection to a spark plug, within a spark plug hole in the cylinder head of a reciprocating engine, outward, to a point at which an ignition cable can be easily installed and removed. The conventional extender 10 includes a cylindrical distal portion 12 that extends within the spark plug hole of the engine (not shown) around the spark plug (additionally not shown) held within a cavity 13 with a spring contact 14 engaging the terminal of the spark plug. The spring contact 14 is connected to an electrode 16 extending to a threaded portion 18 at a distal end 20 of the extender 10. Insulation is provided by an outer ceramic insulator 26 extending around the spark plug (not shown) and the spring contact 14, an inner ceramic insulator 21 extending along the electrode 16, a distal PTFE insulator 22 extending over the inner distal ceramic insulator 21 and over a portion of the proximal ceramic insulator 20, a proximal PTFE insulator 24 extending over another portion of the proximal ceramic insulator 20, and an outer distal ceramic insulator 26 extending over the distal PTFE insulator 22. These insulating components 28 are not overmolded, but are instead formed and machined to fit together as shown.
The patent literature includes descriptions, which do not apply to the device shown in FIG. 1, of two-component insulating systems in which the outer component is formed from a material composing PPS (polyphenylene sulfide). In one example, a housing for an ignition coil assembly is molded of a material selected from a group including PPS, to which a reinforcing filler is added, with the housing forming the outer layer of a two-component insulation system. The inner layer is formed by an insulating oil, in which the ignition coil is dipped to be held within a groove inside the housing. In another example, an insulated wire includes a conductor and at least two insulating layers provided on the outer periphery of the conductor. The inner insulating layer is composed of a polyolefin compound, while the outer insulating layer is composed of a single substance or a blend of substances taken from a group including PPS.